Graphene oxide (GO) is a versatile, solution-processable candidate for next-generation, large area, ultra-thin electronics, optoelectronics, energy conversion and storage technologies. The ability to tune and spatially control the oxygen functionality in GO structures may be useful in in opening up band gaps comparable to those of silicon (˜1 eV) for applications in digital electronics and photonics. Such control may also be desirable in technologies based on green and sustainable catalysts, metal/semiconductor GO composites, and/or chemical/biological sensors, which utilize the rich and interactive oxygen framework in a number of ways. However, use of GO in these devices has been limited by the material's inherent chemical inhomogeneity and structural disorder due to, for example, harsh environments, and the inability to exercise spatial control over oxygen groups under present synthetic protocols. These processing limitations result in large optical gaps (−5.6 eV) and poor electronic conductivity, affecting device performance unfavorably. Given the high impact of controlled oxygen functionalization on an increasing number of applications utilizing GO, developing methods that preserve the oxygen functionality and yet enable enhancement of the optical and electronic properties would be desirable in certain applications.
One approach often used to produce GO structures on a large scale is the Hummers' method, which typically renders an oxygen concentration of ˜30-35 at %. To date, many methods to improve the sheet characteristics of as-synthesized GO structures have been reported, but many of these improvements have come at the expense of oxygen content. One such procedure is to produce reduced GO (rGO) with ˜8 at % oxygen. Alternatively, several groups have attempted careful hydrothermal treatments under alkaline or acidic conditions, achieving partial success in conserving oxygen functionality (˜15-20 at %) with improved sheet properties. Other approaches include controlled chemical functionalization methods such as dissociating oxygen molecules in ultra-high vacuum to achieve selective epoxy functionalization, the use of local reduction methods with nanometer resolution and thermal annealing at 750° C. in vacuum to produce graphene monoxide. However, these techniques generally employ expensive ultra-high vacuum set-ups and high temperature systems, making them less amenable to large-scale processing of GO sheets.